Lake-wide phytoplankton production and abundance in the Upper Great Lakes: 2010-2013

Lake-wide phytoplankton chlorophyll a concentrations and primary production were determined for lakes Huron, Michigan, and Superior in 2010-2013. Chlorophyll a concentrations were determined using MODIS imagery with a color-producing agent algorithm and primary production with the Great Lakes Production Model using remotely sensed and empirically derived input from the Upper Great Lakes. The new chlorophyll a and primary production estimates agreed well with field measurements. Lake-wide mean chlorophyll a concentrations determined from observations in all 12 months were highest in Lake Superior (mean = 0.99 mg/m3), intermediate in Lake Michigan (mean = 0.88 mg/m3), and lowest in Lake Huron (mean = 0.77 mg/m3). In Lake Superior, a gradient in chlorophyll a concentrations was noted from the shallow zone (0-30 m, mean = 1.57 mg/m3) to the deep-water zone (> 150 m, mean = 0.94 mg/m3). However, in Lake Michigan, no differences in mean chlorophyll a concentrations were noted in shallow-, mid-, or deep-water zones (means, 0.83, 0.86, 0.90 mg/m3, respectively). Lake-wide areal integrated primary production rates in lakes Huron, Michigan, and Superior were not significantly different for the 2010-2013 period (means, 216, 259, and 228 mg C/m2/d, respectively). Also, primary production in all depth zones (shallow, mid, and deep) were similar across lakes. Annual whole-lake phytoplankton carbon fixation values for 2010-2013 ranged from 4.4 to 5.7 Tg/y for Lake Huron, 5.0-7.2 Tg/y for Lake Michigan, and 6.4-9.5 Tg/y for Lake Superior.